text:
What is the typical angle of attack aircraft fly at and at what angle of attack do they stall?
At what angles of attack do aircraft typically fly at? How much of a margin is there before aircraft stall due to an increase of an angle attack due to factors such as gusts or rotation of the wing section due to deformation?

what kind of aircraft ? Fighters like the F-18, MiG-29, Su-27 can do 80º, 120º and 180º AoA for brief momments...

I was thinking along the lines of commercial aircraft.

It depends basically on the wing section. Some of them stall at a higher angle of attack than others...
To quote typical values (for wing + body, since not only the wing gives lift...) a given plane may achieve the flattest glide (best range, L/D = 12, at 155 knots) with an angle of attack of 4º. If you wish to fly slower, you can do it at 115 knots, with L/D = 8, and a steeper AoA (13º) or you can choose to fly faster, at 210 knots, always with L/D = 8, but with an AoA of 1.5º.

Thus, and except for the best L/D, there are always two angles of attack for the same L/D, one of them steep (slower flight) or flat (fast flight)...
The stall, for the example I'm quoting (book 'Mechanics of Flight, by A.C. Kermode)' takes place at 15º...

@mins  Thanks for 'embedding the image'...

The AOA is negative during the ground roll in order to maximize the aircraft's velocity and the angle will only be positive once this minimal speed is reached and the front landing gear detaches from the ground due to the lift. Is it correct that?

So, if the AOA for that aircraft is less than ~-2º or greater than ~+20º, the aircraft will start moving backwards?

It depends. These factors influence the flight angle of attack:

Altitude. Higher up the air is thinner, so the flight angle of attack tends to be higher.
Aircraft speed. Fast airplanes sometimes need to limit lift by flying at a slightly negative angle of attack.
Wing camber and incidence. High camber means high lift already at zero angle of attack. Extreme cases like the B-52 need to fly with a visible nose-down attitude when flying low and fast or when the high lift devices are deployed.
Aircraft weight. This is both influenced by aircraft mass and the load factor flown.
Wing sweep. Higher sweep means lower lift curve slope, so a higher angle of attack is needed. Thankfully, stalling is also delayed, in extreme cases (delta wing) above 30°.
Aspect ratio. A lower aspect ratio works in similar ways to sweep: Stall is delayed to higher angles. Gliders, on the other hand, stall already at 10° - 15° angle of attack (depending on flap settings).
Mach number: At transsonic speeds the developing shocks on the wing can stall the aircraft at much lower angles than those usual at low speed.
Rate of angle of attack change. In dynamic manoeuvers the stall lift coefficient could be pushed up by 50%.
Directional stability: The F-4 Phantom II is limited to 23° angle of attack simply because the vertical tail will be insufficient at higher angles. Here the aircraft does not stall but is artificially limited.

Normally, the designer tries to set the wing incidence such that the  fuselage is level at the design speed and altitude. The wing angle of attack is then also near zero or at low, single-digit degrees. The stall angle of attack, however, is all over the place, from high single-digit values (high-speed stall) up to more than 30° (highly swept, low aspect ratio configuration with vortex lift).

An aircraft typically flies at angles of attack range about 2-5 degrees, depending of the flight altitude, speed and g-load of maneuver. It's much more (about 10-12 degrees) when flight speed is near to take-off and landing speed. The critical angle of attack when an aircraft goes to stall usually is about 15 degrees, mainly depending of the wing plane form, flight Mach number, the wing section profile and flaps position. So the safety margin is about 10 degrees, but the margin drastically decreases in take-off and landing. Therefore it's dangerous when an aircraft, say, is in approach to landing while undergoes a vertical gust that may lead the aircraft into stall.


text:
Is it allowed to let the engine of an aircraft idle without a pilot in the plane. (For both helicopters and aeroplanes)
Is it allowed to let the engine of an aircraft idle without a pilot in the plane. (For both helicopters and aircr).
Would there be a difference between a C172 and a 737?

There appear to be no specific regulations against it.

Go search up the video of a pilotless airplane that circled over (Perth?) for a couple hours one day, many years ago...  Pilot was hand starting, brakes and/or chocks weren't set right, throttle was up a little because hard to start -- and away it went, took off by itself and flew until out of fuel.

I mean technically ramp personnel can taxi the plane, so I guess.. yes

In the state of Washington, it is not permitted under RCW 46.61.600.  (An airplane is a motor vehicle under the definition found at RCW 46.04.320; most of RCW 46.61 only applies to vehicles operating on public highways, but this one is applicable everywhere.)  I'm not aware of any instances of enforcement, but if your plane gets stolen while you're letting it warm up, it's something to watch out for.

It depends on the fed.  One may think it's fine, the other may think it's careless and reckless.

You won't see it done in the fixed wing world unless the aircraft is tied down or otherwise securely restrained (like when you tie off the tail to something when hand starting your no-starter taildragger; some pilots just use chocks or parking brakes to hand bomb their airplane, but it's a terrible idea).
However, it's common in the helicopter world especially in bush operations.  With the collective and cyclic friction locks tightened down and the engine in ground idle, it can't really go anywhere and a pilot who lands in a remote area without assistance to hook up a sling load or lug something on board will often do it without shutting down.

I think it's fairly common for airliner engines to be run by ground staff, without an actual pilot in the plane.

Technically yes, but there will be a mechanic who is specifically qualified for ground runs and taxiing in the pilot's seat.

@JohnK. The bush helicopter example is good, but probably not doesn't speak one way or another about regulations.

Well, there is no regulation as such, except for the one for careless operation, which is generally something that will only get applied after an incident in a case like this.

Even if you have the plane tied down while hand-propping it, there will still be a few seconds (or longer, depending on your agility) where you have to leave it idling while you get out to untie it.

This is a problem, although once it's running at idle the risks aren't that great.  My solution when flying hand started airplanes was to tie one end of a 50ft rope to something by the cockpit door or in the cockpit, loop it around a fence post or something in the ground, tie a slip knot at the tailwheel, with the end of the rope back in the cockpit.   Just pull the end to release the slip knot, then reel the entire thing in.   My current plane has a starter but I still carry a 50 ft lightweight rope in the baggage cmpt for this purpose in case of a dead battery or failed starter.

I'd say no, you're likely to be busted under 91.13...

14 CFR § 91.13 - Careless or reckless operation
(a)Aircraft operations for the purpose of air navigation. No person
  may operate an aircraft in a careless or reckless manner so as to
  endanger the life or property of another.

Having had a parking brake slip on a small GA aircraft once or twice myself, I can say its generally a bad idea regardless of regulations.

It would be very difficult for a lone pilot to hand prop start an aircraft without this occurring for some span of time, which would lead me to conclude that it is not forbidden.

Logic cannot be denied...

Glider pilots found a way to disconnect their glider from a tow rope without leaving the cockpit, so the same approach could be used here.

@Harper ... but logic can be incomplete. See JohnK's comment on his post re a 50 foot rope. He is not in the cockpit at some stage when the engine is running (logic passes) but the aircraft is never restrained when he is not in it (logic still passes by dinna tell all the tale).

Generally speaking, no.  Legal or not, it is a very bad idea.
To add some detail, in the Navy we would "hot switch" pilots occasionally in the EA-6B - shutting down the left engine on the pilot side, but leaving the right one running.  In these cases the plane was chocked, (chained when shipboard) and there was always an NFO in the right seat to monitor the engine and shut down if needed during the minute or so it would take the next pilot to climb in.
Otherwise the only other time you would not have a pilot in the plane is when a turn qualified engine mechanic was there instead, supporting maintenance.  I would imagine similar policies are in effect at the airlines.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Technical factors to consider for retrofitting aerial refueling for commericial aircraft
What are the factor that need to be taken into account to retrofit and an airliner like an a330 or 777 or maybe even a business jet like a global 5000 to an aerial refuelable (receiving) aircraft. Is it even possible?

If you're asking why commercial airliners aren't fitted for midair refuelling, see this question

It is possible, although expensive. Several aerial tankers currently in service are based on airliners, for example the Airbus A330 MRTT:

As Wikipedia states:

In November 2015, it was announced that an RAF A330 MRTT would be refitted to carry government ministers and members of the Royal Family on official visits. The refit would cost £10m but would save around £775,000 annually compared to the current practice of chartering flights. The aircraft, nicknamed "Cam Force One" by some in the media, will be fitted with 158 seats.[38] The aircraft entered service on 6 May 2016, with the then Prime Minister David Cameron making his first flight on it to visit the 2016 Warsaw summit.

So we know the airframe has enough commonality with the original airliner design to convert from one role to another. After all, Airbus produces the A330 MRTTs as standard A330s, which are then delivered to the Airbus Defense and Space plant in Getafe (near Madrid, Spain) where the refuelling systems are fitted.
As for what it involves, the redesign itself is the most complex part, since it involves aerodynamic changes due to, in this case, the boom. In fact Airbus suffered a mishap during testing where the boom broke off due to aerodynamic forces (I have heard the root cause was in the software laws of the boom control system, but don't quote me on that).
Other than that, adding a boom operator crew station and housing more fuel tanks inside the fuselage is fairly straightforward.

I think the question is about adapting an airliner to receive fuel, not to be a tanker. The wording is a little unclear, though.

@Pondlife that may have been added after I started typing, but fair enough.

Not only are the MRTTs adapted from airliners, they are actually used in commercial service (5 of the RAF purchased MRTTs are available for lease to commercial providers, https://www.airtanker.co.uk/leasing) Although the RAF MRTTs don't have a boom.

Yes, of course this is possible.
The main factor taken into account is pilot training. Mid-air refuelling puts the receiving aircraft into an unstable position which needs to be held manually for the duration of the operation. Without proper training, the refuelling operation will carry a high risk of being unsuccessful. Mechanically the modification is simple: Add some fuel lines, valves and the standard receptacle for the Air Force boom system of refuelling (at the fuel mass needed only the boom system would make sense).
The best example is a Boeing 747-200 B which has been converted as the US presidential transport. The fuel receptacle sits ahead of the cockpit on the upper side of the aircraft's forebody. From the linked site:

Capable of refueling midair, Air Force One has unlimited range and can carry the President wherever he needs to travel.

modified Boeing 747-200 being refuelled by a KC-135 (picture source)
However, this capability has never been used with any US president on board and is likely to be deleted from the next version of the plane. From Popular Mechanics:

As part of the effort to cut costs by $1 billion, aerial refueling was cut from the program as well, as reported by Defense One earlier this month. Proponents of the cut argue that aerial refueling is not necessary considering no president has ever used the capability, not even George W. Bush who loitered over the Gulf of Mexico in Air Force One for eight hours after the 9/11 attacks. Opponents of removing mid-air refueling say that the ability to take on fuel and fly for long periods of time, even days, is vital to ensure the government can continue operating in a crisis, including nuclear war.

I don't think that the physical / mechanical modifications to the aircraft would be that big. You essentially just need a receptacle at the front and a fuel line from the receptacle to the tank(s).
Obviously, on transport category aircraft, everything has to be super-safe, so everything would have to be multiply redundant. E.g. two receptacles, each with two fuel lines running along both sides of the fuselage into at least two different tanks.
The problem lies elsewhere: aerial refueling is an extremely dangerous and complicated maneuver with very small safety margins. It requires an amount of constant, regular practice that is just not financially viable for an airline operator. Also, there is no way that such a dangerous procedure would ever be certified by any agency.
There are a couple of prototypes of military UCAVs that are capable of autonomous aerial refueling. Maybe, when the military has demonstrated a couple of thousand autonomous aerial refuelings without any incident, regulators might think about certifying such a software. But that is way into the future.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Do airlines in the US or UK have to pay fuel taxes?
Do airlines in the US or UK have to pay fuel taxes?
When looking at Jet-A prices on the Shell website, for example, it's unclear if the listed prices include taxes. Do they?

Why do you believe they wouldn't be subject to local and federal taxes?

Have you seen this and this (and perhaps this)?

@mins your second link is 14 years old, tax rules can and do change more often than that. The third took me to a site giving guidance on when to use capital letters. Also the way your comment is worded is highly obnoxious.

@Notts90:  I didn't want to elaborate on that, but since you ask... well, this question indeed shows no research at all, for that it could be downvoted, I didn''t. It is also expected US/UK are correctly written, it's a modest effort.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Fine for operating not single-pilot certified jet with one pilot
Are there any clear-cut fines for flying an aircraft like a Global 5000 which is not single-pilot certified by a single pilot?
And what would be the probability of being caught and how would they catch you?

FAA penalties are not like automobile speeding tickets: "5 to 10mph above: $50 fine;  11 to 20mph above: $200 fine".  Instead, once a violation has been found, the penalty can be arbitrary and wide-ranging, from required retraining, suspended licenses, revocation of your  license, or in extreme cases, referral for criminal prosecution.

FAA Order 2150-3B outlines the enforcement actions that the FAA may take. Here are a few:

Civil penalties (cash fines) of up to \$50,000 for individuals and small businesses and up to $400,000 for larger businesses
Suspension or revocation of your license
Seizure of the aircraft
Lien on the aircraft up to the amount of the civil penalty
Medical denials

What exactly the FAA decides to do when it finds out is up to the FAA and subject to the surrounding circumstances. If you moved the airplane from Podunk A 10 miles to Podunk B, or if you decided to buzz the Whitehouse and wave to the President, these would be evaluated differently.
At the very least your license would probably be revoked or suspended, the FAA doesn't take that very lightly (it is not done often). Most likely you would not be given jail time, as this particular violation doesn't fall under one of the criminal violations (see page 4-39 in linked document).
As far as probability, it would be high, as John K says, you need to be around a lot of ground people (fueling, movement, etc). They would catch you by noticing that you are the only pilot in the cockpit when the aircraft starts moving. Not to mention that the aircraft is not single-pilot certified for a reason, it would be difficult to fly it by yourself (not necessarily impossible, but you will probably be noticed by ATC as you try to do a lot more workload than your resources allow).

I don't think it's hard to fly alone at all if the pilot is decently proficient and sharp.  When I was flying RJs I had sim access with motion off (I could run it if it wasn't in use and I had to leave the bridge down) but with visuals and everything else working, and used to practice flying it alone all the time.  Very useful skill set to have for an incapacitated crew situation.

@JohnK Just curious why access with motion off is given? Why weren't you allowed to use the full sim?

Because the sim accumulates chargeable operating hours when the motion is on but not when it's just the electronics powered up and it's sitting stationary with the bridge down and door open.  To be run with full motion there had to be a qualified instructor running it with a paying customer.  The training center where it was located was close by and it was an unofficial courtesy afforded to company pilots when the sim was idle.

Couldn't disagree more about the probability of being caught. If you don't crash or bust airspace you can get away with pretty much anything for a very long time.

According to FAA Order 2150-3B in Appendix B (penalty guidelines) the recommended penalty for "Failure to comply with operating limitation" is a 30 to 90 day license suspension. That is what I would expect would happen in real life if the FAA investigator thought that the pilot had no good reason for operating without a co-pilot. If there was some good reason and the pilot's record was clean otherwise, they might change it to a warning.
I disagree with the other answers that claim it would be quickly reported. Unless an informed passenger noticed it and reported it, I doubt it would get reported by anyone else. The fuel guys have no idea what operating limitations are or who is operating the plane. In many cases, crew and passengers are long gone by the time the fuel truck pulls up. For the fuel truck to deal with just one guy or to fuel an unoccupied aircraft is commonplace. For all the fuel truck guy knows, there could be crew inside the aircraft doing stuff. He has absolutely no idea what the operating situation of the aircraft is.

What might be accepted reasons for "operating without a co-pilot"?

They've died? They've fallen out of the aircraft?

The probability of getting caught would be pretty high because you would be around ramp crew all the time and somebody would notice there's only one pilot aboard when there are normally always 2.  But you could probably get away with it a few times.
Penalty for that kind of thing would depend on the circumstances and motivations. At minimum a fine of a couple grand and a license suspension for a number of months.  A professional pilot who depends on his/her license would be insane to do it unless it was for life and death reasons (like escaping from some dangerous place).
Possibly jail time.  Authorities in the 80s and 90s started to revise regulations to add the option of criminal liability for certain violations on top of administrative punishments, to give the rules more bite.

So you are saying putting a guy (non pilot) in a fake uniform next to you on the copilot seat would drastically reduce the risk?

Yes in theory.  Then it would just come down to whether the owner of the airplane discovers it, or ground personnel notices that your FO appears to know absolutely nothing about airplanes and just stands around doing squat and keeping his mouth shut as you handle every detail.  That would stick out like a sore thumb because FOs normally do all the grunt work.  For every hour of flying a jet, there is an hour of work done on the ground and a lot of interfacing with folks one on one, especially a corporate a/c.  It would be hard to hide the truth for long.

It seems highly unlikely that you would be caught if you flew a 2 crew aircraft as a single pilot. The real issue would be what would happen if there was an accident, even a small non-injury accident, and there was an investigation.  And the bigger issue would not be what the FAA would do but what the insurance company, or aircraft owner, would do.


text:
How is flight planning performed with short turnaround times?
For low cost carrier short-haul flight such as Dortmund-London I have experienced multiple times that turnaround times are around 20-25 minutes. In such a short time what is included in the flight planning of the pilots. This time seems very short to perform flight planning, preparation etc. Is it generally the case that for repeating flight planning efforts and necessity are reduced by a significant amount?

Doesn't a computer just kind of burp out all the solutions to the relevant variables (ETA, etc)?

The main reason why turnaround times can be that short is that pilots brief all flights of the day in the morning before the first flight.
This briefing is typically done in the crew room at the airport where the pilots are based. It typically starts about an hour or more before the first flight since there is a lot to cover:

Routes: the flight routes for all flights would already be planned by the dispatch department by this time. They are also filed with ATC by dispatch, so the flight crew only has to review it. This review involves discussing terrain and other possible threats as well as possible diversion airports in case of problems.

Fuel: the required fuel calculation is also done by dispatch, but the final amount of fuel to take is at the captains discretion, so the pilots would discuss possible reasons for taking more fuel (e.g. weather, expected delays at busy airports).
The final weight and balance is only known once the gate closes since passengers might not show up for a flight or additional passengers are booked onto the flight, which is not yet known in the morning. So this will be done during the turnaround.

Weather: the briefing package will contain the METAR (current weather) and TAF (forecast weather) for all airports visited during the day and all possible diversion airports. The crew will carefully review the expected weather at the expected times spent at each airport. The prevailing wind direction typically dictates which runways are in use for takeoff and landing. The crew would discuss which departure and arrival procedures they expect at each airport.
The crew will also discuss en-route weather, like e.g. thunderstorms (might require deviating from the planned route) or expected clear air turbulence (so they can brief the cabin crew about this).

Aircraft: since an aircraft can be dispatched with some items inoperative (Minimum Equipment List), the crew will review the information about the aircraft they are about to fly. This means they are aware of any missing or inoperative items and their consequences. Some airlines also have aircraft with different equipment or engines installed (e.g. A320ceo and A320neo) and the crew will brief the differences in operation (if any).

NOTAMs: these notices to airmen contain important information about the current situation at airports or for specific airspaces. This could be an airspace closed during a special event, it could be a taxiway closed for maintenance, it could be an unavailable approach because some equipment is broken, etc. The crew will go through all NOTAMs and discuss which ones are relevant for the flights today so they are already prepared.

Since all of these things are already taken care of, the actual turnaround can be pretty short. After shutting down the engines, one pilot will start loading the next flight plan into the flight management computer (FMC), which can usually be done via ACARS or loaded from a stored company route, and review that all waypoints and altitude/speed constraints are loaded correctly. In the meanwhile, the other pilot will do the external walk-around. Once that is done, the pilot flying will brief the pilot monitoring about expected taxi routes, the takeoff (including possible rejected takeoff) and the expected departure procedure (including possible return or diversion in case of an engine failure). An experienced crew can do this briefing in less than 5 minutes.
Once the gate is closed, the captain will get the final load sheet and will verify that everything is within limits. Now both pilots will independently do the takeoff performance calculation and compare the results. If they match, the values are entered into the FMC and you are good to go.
The limiting factor for turnaround times is usually the required time for disembarking, re-fueling and boarding. Regional airlines with short turnaround times do not load any trolleys for food and beverages during these turnarounds (they are all loaded in the morning) and only do a very superficial cabin cleaning (if any) to minimize time on the ground.
Aircraft manufacturers publish time estimates for these activities in their airport planning documents. Here is an example for an Airbus A320 without refueling (source):

They estimate 22 minutes without refueling, so anything shorter than that is really quite fast. With refueling of 20,000 litres (which is quite a lot, definitely more than you would need for a short haul flight), they estimate 44 minutes:

Airlines have dedicated dispatch/ops departments that do flight planning. Everything is done in advance, and the pilots simply receive all the needed documents prior to departure. The pilots simply have to do the final weight, balance and performance calculations and input that data into the flight computer, then they are ready to go. Planning of route, required fuel, diplomatic clearances if required, etc. etc. is all done by someone else.

To add to Ymb1's comment, expounding on your personal experience might also help us craft a better answer.  For example, if you are a student pilot just starting cross countries it is understandable that 20 minutes might not seem like a lot of time.  And it isn't, if you are planning from scratch for a destination you've never been to before.
However, for an airline pilot flying a short hop they have done hundreds of times before there really isn't even any "planning" involved.  Your navigation system will have the route already loaded, you just need to scroll to it and activate.  You are already familiar with the airfield and approaches, and both pilots and dispatch know the fuel requirements.  Weather at your destination will likely be pushed to you via data link, same likely for ATIS, clearance, and your dispatch release.
What might seem complex at first for a novice becomes fairly routine when you've done it long enough.  Realistically, most of that time during turnaround that you might think of as used for planning will be spent waiting on fuel and pax to load, and running through checklists.


text:
Why is alcoholic gasoline such a showstopper for aviation?
One of the main reasons the common avgas grades are still full of 3-plumba-3,3-diethylpentane is the incompatibility of many aircraft fuel systems with the oxygenates (primarily ethanol, with some ETBE) used as octane boosters in mogas, as mentioned (for instance) here:

[...]  87UL/E0 (similar fuels are called 82UL or 85UL) -- This is a tightly specified form of motor gasoline (mogas) -- without any ethanol or oxygenates in it, as many aircraft fuel systems aren't compatible with ethanol -- that is used in low-compression aviation piston engines mounted in airframes certified or STCed for operation on motor gasoline.  [...]

Bolding in original; emphatic italics added.
But the automotive industry had the exact same problem, and, yet, adapted easily to the advent of alcoholic unleaded gasoline (namely, by replacing incompatible fuel lines and seals and whatnot with ones not dissolved by ethanol).  So why are oxygenates so much more of a stumbling block for aircraft fuel systems and engines?

Related: Why are we still putting lead in our fuel? and What are some of the differences between piston engines used in aircraft and automobiles?

The modifications required are just not economically viable.
The main issue is vapor lock, because ethanol has a lower vapor pressure (i.e. more likely to vaporize) than gasoline.  Worse, mogas ethanol levels are varied to achieve ideal vapor pressure for different temperatures.  This is fine for cars that go through a tank of gas every week or two, over a relatively small temperature range, but a serious problem for planes where the gas may sit for months and then experience a wide temperature range at different altitudes in a single flight.
Vapor pressure matters because engine-driven fuel pumps, which are the norm on planes, pull fuel through the fuel lines.  Especially when combined with low wing tanks, ethanol may vaporize in the lines and block any further fuel flow, which is a far more serious problem for a plane than for a car.  Pure gasoline has a high enough vapor pressure that doesn't happen.  When ethanol was first added to mogas, carmakers solved this by moving the fuel pumps to the tank so the fuel is instead pushed through the fuel lines and therefore won't vaporize regardless of its vapor pressure, and given normal fleet turnover, that was the norm within a few years.  Some planes do have tank boost pumps like cars, but they are usually not intended to be run full-time; ethanol would require tank boost pumps that can run full time, which means either replacing the existing ones or adding new ones.
Ethanol is also more corrosive than gasoline.  Using ethanol regularly may mean replacing fuel pumps (both engine and, if applicable, tank), fuel lines, seals, injectors or carbs, etc.  To make such modifications, you'll need an STC for each.  Developing an STC is expensive and the market is quite limited, so the companies selling them need to charge a lot to recover their costs--on top of the high cost of the parts themselves, which have the same issues.  Also, while many engines were retroactively rated for mogas (even with ethanol in some cases), you still need an expensive STC to change the old placards that require avgas.
Also, while not directly related to ethanol, mogas doesn't contain lead.  Older airplane engines still require a tank of leaded avgas occasionally to lubricate valve seats and guides.  That can usually be fixed by replacing certain parts with newer ones made from newer materials, but that's not cheap either and usually best delayed until the next overhaul.  Until then, you can't run mogas full-time, regardless of the ethanol content.
Once you add up all these costs, retrofitting most GA aircraft for ethanol could easily end up being more than the planes are worth.

Don't we have to worry about alchohol attracting water also? Engines don't run well when they get a slug of water going thru the system.  https://en.wikipedia.org/wiki/Dry_gas

Water is a problem with pure gasoline because they separate, so the engine receives a slug of pure water and dies suddenly. Adding ethanol makes gasoline and water miscible, so the engine is still getting mostly fuel and keeps running, though a bit rough like it's too far lean of peak. That's not desirable from a maintenance perspective, of course, but it's less likely to kill you.

The automotive industry "adapted readily" because cars are commonly replaced with a service life of five or, at most, ten year.  Aircraft are expected to last much longer than that, so the old technology hangs on.

Cars are neither replaced as quick, nor use up the fuel as quick. Faster than GA aircraft probably yes, but there are many people who only burn through a couple of tanks of gas a year, and plenty of twenty year old cars around.

@ZeissIkon the car industry "adapted readily" because they were given no choice in the matter. Adapt or die was basically the message. With light aircraft (now the only gasoline powered ones in common use) it'd mean death for general aviation as replacing the entire fleet over the span of a few years would be impossible.

@JanHudec  You mean vs. nearly the entire GA fleet in the USA that averages 30+ years old and thinks nothing of regular use of aircraft fifty years old.  A guy with a 1960s Chevy is the rare bird who stores and drives it like an airplane.

@ZeissIkon, I mean vs. what you claimed in the comment.

The main issue, the one that bans ethanol blend fuel for use under the autofuel STC, is the effects of ethanol on rubber components in the fuel system.  Ethanol is also mildly corrosive to aluminum but nowhere near as bad as methanol, which will dissolve a fuel tank in days (methanol powered race cars race and then purge their fuel systems right away).
10% ethanol in a fuel tank won't generally hurt it.  If you install ethanol compatible hoses and seals (especially the carburetor float seal) you can run ethanol blend fuel mogas and the airplane won't care, notwithstanding the other issues like the water absorption tendency.  This is an option for homebuilts that aren't restricted in materials used in the fuel system, and can be a good safety measure against accidental adding of mogas with ethanol.
There is a quickie test for finding ethanol in gas.  Add fuel to a test tube like container, add some water, which goes to the bottom, mark the water line, then shake the tube.  After the mix settles out, if the amount of water has magically increased, that's water plus ethanol mixed. I do that test if I'm using mogas from an unconfirmed source.

So why can't the compatible-materials solution be used for all piston aircraft, instead of just homebuilts?

Also, where did you find mogas that doesn't have ethanol in it?

@sean that depends on where you are. In my country mogas without ethanol is available at twice the price of mogas with ethanol.

You can only use approved materials so it depends on if you can find them.  For example, the MIL-SPEC that hoses are made to doesn't make alcohol resistance a requirement because they assume the use of avgas.  Traditionally, premium fuel is ethanol free, at least in Canada.

@vasin1987: Which country is that?

The Rotax line of engines are engineered to use premium automotive pump gasoline with 10% ethanol. Their engines can also use AVgas, but that tends to load the oil with lead and requires more frequent oil changes per Rotax. Rotax is a major player in aviation especially in the lighter aircraft and LSA.
When you hear that mogas with ethanol is bad news or can't work due to vapor lock or because it is hydrophilic, just understand that it is mostly obsolete info. However, it is accurate that the tried and true Lycoming and Continental engines are designed to be run at low rpm and to use 100 low lead AVgas. With that said, I know guys who run premium mogas with ethanol (and often mixed with AVgas) in their 8.5:1 Lycoming engines without any problems...so far. :)

Not seeing how this post answers the stated question...

@Ralph I do. He says the question is based on obsolete info. +1

@Ralph Let me clarify. I should have started by saying that premium grade (AKI 91) pump gas with 10% ethanol is not a showstopper. The tried and true 1940s technology engines like Lycoming and Continental are designed for aviation gasoline with 100LL. (Older engines were designed for 80LL) Newer engine makers are modernizing aviation engines to use premium E10 pump gas. ULPower is a consortium of Belgian companies that are doing it. So is the Austrian BRP Rotax. Example: https://ulpower.com/en/engines/ul520  Change starts in experimental aircraft and will move to certified later.

Also see: https://www.kitplanes.com/2021-engine-buyers-guide-flat-four-stroke-gasoline/

It's not just big twins that have "high compression" or use turbos. Many four and six seat engines have higher compression engines also without turbos.  My Lycoming O-360-A1F6D has no turbo. has 8.5:1 compression ratio cylinders and needs 100LL to prevent early detonation.
https://www.lycoming.com/sites/default/files/O-HO-IO-HIO-AIO%20%26%20TIO-360%20Oper%20Manual%2060297-12.pdf
O-360-A series

FAA Type Certificate ...................................... 286
Rated horsepower ......................................... 180
Rated speed, RPM.......................................... 2700
Bore, inches.................................................... 5.125
Stroke, inches.................................................. 4.375
Displacement, cubic inches.............................  361.0
Compression ratio ..........................................  8.5:1

(The -A1F6D indicates things like hollow shaft for oil pressure to drive the constant speed propeller via governor, counterweights on the crankcase to balance the cylinders, dual magneto vs 2 separate magnetos).
And if you look at page pdf page 42 (marked as 3-10), almost all the O-360 engines need higher octane fuel:

FUEL AND OIL                                        *Aviation Grade Fuel
Model Series                                        Minimum Grade
O-360-B, -D                                         80/87
O-360-A1P, -C1F, -C4F; HO-360-C1A                   91/96
O-360-C, -F; HO-360-A, -B; IO-360-B, -E; HIO-360-B  91/96 or 100/130
O-360-J2A                                           91/96 or 100/100LL
IO-360-L2A, -M1A, -M1B                              91/96 or 100LL
HIO-360-G1A 91/96 or 100LL
O-360-A, -C1G, -C4P, -A1H6; TIO-360-C1A6D           100/100LL
IO-360-B1G6, -C1G6, -J, -K2A, -A1D6D, -A3B6, -A3D6D;
HIO-360-A1B                                         100/100LL
AIO-360-A, -B; IO-360-A, -C, -D, -F                 100/130
HIO-360-A, -C, -D, -E, -F                           100/130
TIO-360-A                                           100/130

The fuel injected version used in the retractable gear version of my plane. IO-360Axxx, has higher ratio cylinders, 8.7:1 and develops 15-20 more horsepower.
Here's a little more info on Leaded Aviation fuel, from https://www.faa.gov/about/initiatives/avgas/

FAA Home ▸ About FAA ▸ Programs & Initiatives ▸ Aviation Gasoline
  Aviation Gasoline
  About Aviation Gasoline
  Subscribe
  Share
  Print
  The Federal Aviation Administration (FAA) shares the Environmental Protection Agency's (EPA) concerns about lead emissions from small aircraft. Owners and operators of more than 167,000 piston-engine aircraft operating in the United States rely on aviation gasoline (avgas) to power their aircraft. Avgas is the only remaining lead-containing transportation fuel. Lead in avgas prevents damaging engine knock, or detonation, that can result in a sudden engine failure. Lead is a toxic substance that can be inhaled or absorbed in the bloodstream, and the FAA and EPA and industry are partnering to remove it from avgas. Avgas emissions have become the largest contributor to the relatively low levels of lead emissions produced in this country.
To help "get the lead out," FAA is supporting the research of alternate fuels at our William J. Hughes Technical Center in Atlantic City. We are working with the aircraft and engine manufacturers, fuel producers, the EPA and industry associations to overcome technical and logistical challenges to developing and deploying a new, unleaded fuel.
The FAA continues to work with EPA to make this a smooth transition and to ensure the supply of aviation gasoline is not interrupted, and that all aircraft can continue to fly.

This follow-up article has more info:

The unleaded fuel disaster - what it means for pilots | Air Facts Journal
  https://airfactsjournal.com/2018/11/the-unleaded-fuel-disaster-what-it-means-for-pilots/
The new timeline focuses on testing of an unleaded fuel being developed by Shell—now the lone participant in PAFI following the elimination of Swift Fuels’ candidate fuel.

Another article, from AOPA  https://www.aopa.org/news-and-media/all-news/2018/october/03/faa-sees-mid-2020-completion-of-unleaded-avgas-project

The FAA had halted testing last spring, calling for Shell and Swift to address concerns that emerged in data gathered in early phase tests.
  In August, following a meeting of the PAFI Steering Group at AOPA Headquarters, AOPA reported on PAFI’s continued progress and plans going forward.
Before flight testing under PAFI resumes, preliminary work “will include clearing material compatibility, durability, detonation, and performance issues,” the FAA said.
Addressing the extension of testing into 2020, the FAA reiterated that “the PAFI mission endures,” noting, “although it will take additional time to realize this goal, it is essential to ensure a viable, safe, and economical fuel is ultimately authorized.”
“AOPA is encouraged to see Shell’s continued commitment and efforts to work on issues and come up with mitigations,” said David Oord, AOPA senior director of regulatory affairs. “We and the other members of the PAFI steering group were pleased to see that early results from their efforts look promising.”
Oord reiterated continued support of the government-industry efforts to identify, test, and authorize a general aviation fleetwide unleaded replacement for 100LL avgas, noting AOPA’s longstanding position that the resulting fuel must not require extensive changes to engines, aircraft systems, or fuel delivery systems.
“Ultimately, we are looking for the best fuel, whether it results from PAFI or other means.The goal is the same, regardless of the path we take to get there.”

I recall seeing a (or some) articles during the Feb 2019 Gov't shutdown saying testing was suspended for an unknown time, so unleaded fuel will not be available for a while.
The higher horse power engines, like the O-540 and IO-540, are 6-cylinder versions of my 4 cylinder engine. So if mine has 180HP/4 cylinders, ~ 45 HP/cylinder, than an O-540 is generating ~ 6x45 = 270HP, and and IO-540 ~ 50 HP/cyl = 300 HP.  Those can be found on 6-seat planes, and the bigger twins.  We all have the same need for 100LL fuel.  My home airport has stopped carrying 87 octave mogas, I presume that demand has dropped, and only carries 100 LL now.  I can't even recall the last airport I was at that had 87 mogas.

Lots of good detail about octane/AKI, compression ratios and lead, but this question is about the italicized part of the quote saying airplanes aren't compatible with ethanol.

Yes, but the alcohol/ethanol had been hashed out already. And this didn't fit in a comment.

No turbo high compression 100LL engines run fine on 92 or 94 octane mogas.  A glider club I used to be in has many thousands of hours on premium mogas in O-360s.

Hmmm... I guess high compression is a relative concept, automotive applications very commonly have CR's of about 10 or more for naturally aspirated engines. In my mind anything below 9 definitely is not a high compression ratio. Detonation in aviation engines @ low CR is simply due to ancient engine design...

There are actually several different things affecting this.
The usage of aviation gasoline
When it comes to aviation gasoline, most volume is used by high-performance engines having turbos. Examples are twin engine airplanes used in line operations. These are made for the higher Octane number and cannot run on lower Octane numbers. (As far as I know, it is currently not possible to create gasoline with high enough Octane numbers for these Engines without using lead, but I might be wrong there).
As these engines are the main volume users and they require high octane fuel, you will find that on "larger" airports Avgas 100LL is readily available. Most smaller planes are certified to use this fuel and, well, as it is available they do. Some airports may offer additional fuel choices, but not necessarily at a lower prices.
In order to run on different fuels you need a STC
A STC (Supplemental type certificate) will cost money to create (sometimes payed for by the aircraft manufacturer) and might require extra costs for the airplane owner. You might need to change some parts in the engine, fuel lines, fuel tanks and so on. World-wide avgas or non-leaded fuel is not necessarily less expensive then 100LL so you might not recoup your investment.
Temperature and elevation
Gasoline is a mixture of several different components. Aviation gasoline is tightly specified to work in low temperatures and at high elevations. Normal domestic fuel is less tightly specified and might evaporate at high elevation and/or freeze at low temperatures. The mix often varies between summer and Winter to keep production costs low.
The way forward
Of course, in due time this might change. Sometimes you can get an Aviation fuel supplier to complement with one of the non-leaded fuel specifications. We did this several years ago at the local glider field and as well as the local municipal Airport (ESSB). The longer time hope is to go for electrical airplanes, but when that happens we will see.

This doesn't really answer the question of why Alcohol fuels aren't used in aviation.

Sorry. I thought it was clear: 1) it is not currently available 2) to make it available has a cost 3) it might not work -- additionally even if was available it might not save any money for the owner.


text:
What is the stall speed of the KC130?
Saw the video of the helicopter chopping off its own refueling probe. That made me wonder what the stall speed of the tanker is, and how difficult it is to fly slow enough for the helis to keep up.

The stall speed is around 95-100 knots for the older F variant, and something like 90-95 knots for the newer J variants.
A KC-130 can refuel between around 100 and 270 knots. The lower end of this is well within the maximum speed of many military helicopters, eg the Pave Hawk, Black Hawk, Chinoook or Sea Stallion.
That leaves an "overlap" of around 20-40 knots, without having to approach too close to either the stall speed of the KC-130 (around 90-95 knots) or the VNE of the helicopter (usually between 140 and 170 knots for a military helicopter). This is enough for aerial refuelling, which usually states a fairly tight bracket for the refuelling speed.
As mentioned here:

The United States Marine Corps has chosen the KC-130J tanker to replace its aging KC-130F tanker fleet. The new KC-130J offers increased utility and much needed improvement in mission performance. As a force multiplier, the J tanker is capable of refueling both fixed wing and rotary wing aircraft as well as conducting rapid ground refueling. The refueling speed envelope has been widened from 100 to 270 knots indicated airspeed, offering more capability and flexibility.

Realize that the power-ON stall speed of a Herk is significantly lower than its power-OFF stall speed (due to the blown wing), and both are sensitive to gross weight & flap setting. Refueling helo's was done, as I recall, at a flap setting that doesn't match a standard landing flap setting. 80% for HAR, either 50% or 100% for landing, if memory serves (pre J model ops).

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What aircraft could make non-stop transatlantic flights in 1958?
According to Wikipedia:

TWA flew to Europe nonstop from O'Hare starting in 1958

The Great Circle Route distance from ORD/KORD to LHR/EGLL is 3953 miles. Other major European airports would have been farther away.
What aircraft were capable of making that non-stop flight in 1958 (also, how long would it have taken)?

Many earlier transatlantic flights stopped in Shannon (SNN / EINN) before or after the Atlantic crossing, they didn't necessarily fly directly to their final destination: "non-stop to Europe" isn't the same as non-stop to Paris, for example. It's still over 3000 miles, but it did cut down the distance (and also importantly, the time) needed for a crossing.

The first scheduled trans-atlantic air service was made possible with Zeppelins. The LZ-127 started flying the route in 1931, mostly to Lakehurst, NJ, or Pernambuco in Brazil, but was disassembled in 1940.
The first airliner which was able to cover the distance (back then it was Berlin - New York) was the Focke-Wulf 200, which in 1938 needed almost 25 hours East-West and 20 hours on the return leg. With its slow cruise speed, wind made a lot of difference. Sadly, the US did not allow Lufthansa to start the scheduled service it had planned to open in 1939. Lufthansa had opened regular air mail services in 1934 between Europe and South America using flying boats and a relay ship in the middle of the Atlantic. Air France added its transatlantic mail service flying from Africa to South America and back.
The first heavier-than-air transatlantic passenger service opened between New York and Marseille in 1939 on Boeing 314 Clippers operated by Pan Am. It crossed the Atlantic between Foynes, Ireland and Botwood, Newfoundland. A British service, also using flying boats, was in preparation but stopped by the beginning of WW II.
In the 1950s, there were already several options for transatlantic air travel, but none of them non-stop from Chicago: Pan Am, TWA, Trans Canada Airlines (TCA), BOAC (successor of Imperial Airways), and Air France all operated large propeller aircraft which covered the distance with refueling steps, typically in Gander (Newfoundland) and Shannon (Ireland). Typical aircraft were the Douglas DC-4 and DC-6, and the Lockheed 149 Constellation, but also the French Latecoere 631 flying boat was used until 1955. Of these airlines, only Pan Am and BOAC serviced O'Hare in 1957, before the first international terminal opened there in the following year.
Still, the prevailing eastward wind made the East-West crossing hard and required airlines to reduce payload, and only the advent of faster  airliners like the Douglas DC-7 (from 1956) and the Lockheed 1649 Starliner (from 1957) made the transatlantic services more reliable and economical. Beginning with the DC-7C, their range was sufficient to support transatlantic service directly from Chicago O'Hare.
In October 1958 the first transatlantic jet airliner service was opened by BOAC using the de Havilland Comet 4, followed shortly after by Pan Am, operating the Boeing 707 and connecting London with New York (with an occasional refueling stop at Gander on westbound flights). O'Hare could only participate in this progress after its main runway was extended to accommodate large jets in June 1960.
Therefore, the most likely airplanes to fly transatlantic directly from O'Hare would have been the DC-7C (but operated by Pan Am, not TWA), the Lockheed L-1049G and the L-1649, which both were operated by TWA. For the flying time, the 3628 miles from JFK/Idlewild to Paris Orly took 14¼ hours with the DC-7C and 14.83 hours with the Lockheed 1649. So it is fair to assume a flying time of 15½ to 16 hours for the slightly longer distance between Heathrow and O'Hare.
Quote from Wikipedia:

In January 1958 Pan American scheduled the DC-7C from Orly to Idlewild
  in 14 hr 15 min; TWA scheduled the 1649 in 14 hr 50 min.

The Wiki quote specifies non-stop - Shannon, Ireland is in Europe, so I would consider a non-stop flight from Chicago to Shannon as qualifying for that. Is Greenland considered Europe? Says he, showing his high-quality American education...

@FreeMan No, Greenland is part of North America, not Europe. It's only 200 miles from Canada at its closest point vs. over 900 miles from (mainland) Norway. However, since it's owned by Denmark, it could be considered politically European, even though it's geographically considered to be part of North America.

@reirab And yet its only 180 mi to Iceland, which is considered Europe. These things tend to be more politically defined than geophysical. And btw, Greenland and Canada are actually only 14.5 miles apart at their closest (see Ellesmere Island).

@DrZ214 Iceland is politically in Europe, but geologically is the border between the North American plate and the European plate, which is why it's so tectonically active. As it happens, Reykjavik is in the western half of Iceland, so it's geologically North American, not European.

Ah, the Lockheed Constellation - The World's Best Tri-Motor! ;)

During WWII  RCAF Ferry Command flew over 9,000 brand new aircraft non-stop from North America to Europe. The crews were returned to NA in what could be termed a passenger service...

s/Lakehurst, NY/Lakehurst, NJ/

@JScarry: I added a link, please follow it.

In 1958, Trans World Airlines operated primarily Lockheed Constellation. Its range is listed as 4,700 nmi, which makes it suitable for that route.
The Wikipedia page about TWA lists when they introduced and retired each type. According to that table the only long range aircraft they had in 1958 was Constellation; B707 only being introduced in 1960.
Similar aircraft that were in service by 1958 with other airlines and had over 4,000 nmi range that is needed for the route were Douglas DC-6A and B, Douglas DC-7, Boeing 377 and already turboprop Bristol Britannia. But TWA did not have any of those types, so they were not used on that particular route.

The Douglas DC-4 was built with transatlantic flights in mind, and would not have been completely phased out (in favor of the DC-6 and -7) in 1958. Swissair ran the DC-4s on the Geneva to New York route (with stopovers: http://www.sr692.com/fleet/14_dc4/index.html) though with the 4200 mile range non-stop flight should have been possible with little weight on board. Perhaps on the return trip to Europe with tail winds?

It looks like the DC-7 Seven Seas variant was the first one to fly regularly transatlantic non-stop.

Also for reference... https://en.wikipedia.org/wiki/Category:Airliners_1940%E2%80%931949

There were regular transatlantic flights even before the 1950s. For example, in 1948, my father was among the passengers in a DC-4 flying the regular route from Madrid to Lima with FAMA, an Argentinian airline. The crossing of the South Atlantic was made from Dakar in Senegal to Natal, in Brazil.

authors: Григорий Туманьян


text:
What is an "emergency squat switch activation"?
I understand what a squat switch does and what it's for: it indicates weight on wheels/skids to indicate that the aircraft is sufficiently on the ground for ground-only things to happen (like deploying thrust reversers on landing) or sufficiently off the ground for air-only things to happen (like retracting landing gear).
I just came across the phrase "emergency squat switch activation" (found in the features list for Flight Vector Map's software) and I don't understand what an "emergency" squat switch activation (or, possibly, "emergency squat switch" activation) might be.
Can someone explain what "emergency squat switch activation" means?

I read their page & I see the phrase used twice, and I have absolutely no idea what they are describing there.  Maybe ping the site & ask them? (Sounds like the kind of nonsense that Chat GPT would come up with, honestly.) Also, the idea that the dispatcher is primary to consider & avert collisions between assets on the road or in the sky seems pretty fanciful to me, so I guess my view of their descriptions isn't particularly favorable.

I'll be responsible for (an end user installation of) some of their software at a new job, so I'm sure I'll learn all about it. I was just trying to get a head start...

I think it's a incorrect word mistake/typo. It should read "emergency squawk activation", that is the software notifies the dispatcher when a transponder is set to an emergency code.
Some aircraft, like the CRJ series, have a landing gear downlock override, that allows retraction of the gear to ensure climb performance in event of a squat switch malfunction, but it is unlikely that this is what is being monitored.

That makes more sense, TBH, but a typo from "squat switch" to "squawk" seems a bit of a stretch. Typos don't often include a mistype and adding a whole new word.

@FreeMan Both of those are concepts the system has to deal with, squat switch status (i.e. air/ground state notification) and squawk. The author got their "squa" terms mixed up. A brain fart might be a better description.

This makes much more sense in context.  @FreeMan, by "new word" do you mean switch?  Because don't some aircraft have a switch that transmits 7700 vs fumbling with number entry in an emergency?

Correct, @MichaelHall, I was referring to a typo from "emergency squawk" to "emergency squat switch" being unusual. I'm not familiar enough with aircraft radios to know if some do or none have an "emergency squawk switch" that one could hit to go direct to 7700. Since there are 3 emergency squawks, would one need 3 buttons? I dunno...

The CRJs use proximity switches/sensors. The downlock override is just for the selector lever that has a solenoid, behind the LDG gear panel, operated by the Proximity Switch Electronics Unit, that blocks the lever on the ground so you can't flip the gear lever up once WOW. If the solenoid craps out or there is a proximity sensor problem, the override button next to the gear lever you work with your thumb forces the solenoid lock for the lever off so you can move the selector once airborne, if it won't move when you select it.

That makes pretty good sense that the software could monitor "squat switch activation" (you can see if the aircraft is on the ground or in the air) and also monitor for an "emergency squawk" so you can see if the transponder is set to the emergency code.  And the rest is just bad copyediting.  Believable scenario!  (Don't put much faith in the "emergency squawk" feature, though; declaring an emergency with ATC verbally is much faster than squawking 7700, and renders the latter unnecessary.)

@RalphJ, sometimes, perhaps, but two of the 3 times I declared an emergency I was unable to break into the radio and squawked first.  (which was easy with a "switch"...)  FYI, this got me wondering so I've posted my own question:  https://aviation.stackexchange.com/questions/98453/do-airliners-have-a-switch-or-other-means-of-rapidly-squawking-emergency

Anyway, probably a freshly hired non-pilot copywriter who didn't understand the distinction wrote that.


text:
How are skis stowed on retractable gear aircraft?
This image of a LC-130 taking off from a snow runway shows that in addition to wheels on the landing gear, it's also been equipped with skis.
Source: Wikimedia Commons.We're getting a lot of use out of this image lately!
How do these skis get stowed when the gear retract?

Do the skis become part of the gear door?
Is there enough room in the gear bay for the skis?
Are modifications to the gear bays necessary to accommodate the skis?
Is there any modification necessary to the movement of the gear to accommodate the skis? (i.e. some gear rotate as they stow. I'm not sure if the C-130s do or not.)

The gear stays out. There is no space for it inside the wells.

For clarification, @PeterKämpf, do the gear retract but the skis stay outside, or do they not retract the gear at all, operating like a fixed gear plane? If they don't retract the gear at all, I can only imagine that would significantly impact range.

The skis partially retract.
Here is an image of one with the gear retracted:

Source: UW Oshkosh

Do the skis become part of the gear door?

From looking at the images with the gear deployed and then the ones with the gear stowed, it appears that the skis do form the gear doors.

Is there enough room in the gear bay for the skis?

No, the skis are not retracted into the aircraft.

Are modifications to the gear bays necessary to accommodate the skis?

It doesn't appear to be, but there may be modifications to the retraction mechanism to allow the wheels to be stowed while the ski is still outside of the aircraft.

Is there any modification necessary to the movement of the gear to accommodate the skis? (i.e. some gear rotate as they stow. I'm not sure if the C-130s do or not.)

It does appear that there is, yes. The ski's can be deployed without the wheels touching the ground, or the skis can remain retracted and the wheels extended for paved runway operations. Take a look at these two photos:

Source: PIntrest
Notice how the wheels are on top of the skis? Now take a look at this one:

Source: FlyIan.net
You notice that the skis are still retracted and the wheels are extended through the skis.
If you want to know what was modified for the gear doors, take a look at this image of a "normal" C-130:

Source: YouTube
Notice how the rear gear door goes a quarter way up the "pontoon"? The version with skis has a fixed panel that replaces the gear door and matches up with the profile of the skis to reduce drag.

I gave you a +1 before the edit. Sadly, I cannot give you 3 more post-edit.

The LC-130 is heavily modified but when the skis retract, they stay outside the aircraft.
Lockheed LC-130 From Wikipedia

"The aircraft are equipped with retractable skis that allow the aircraft to land on snow and ice as well as on conventional runways."

The skis retract until they are almost flush

"The skis retract until they are almost flush with the fuselage during flight, and they can also retract the skis and deploy regular wheels."

LC-130 in flight

source: http://www.nzff.org/viewtopic.php?t=13402&p=8272160

source: http://www.vaq34.com/lc130list/c-130h.htm

Please credit the sources of your images.

The first image is a screenshot from a flight simulator...


text:
Do most commercial jets have a negative lifting body?
I took a look at some example airfoils and noticed they all seem to have a downward hook at the end. I believe this draws the air downwards, creating a reaction force upwards: lift.
Now here is a typical wide-body jet profile:

Notice how the fuselage points upwards at the tail. I'm not talking about the vertical stabilizer, not the horizontal stabilizers either. I'm talking about the fuselage getting narrower and narrow at the tail. It tapers to a point, but the taper flows upwards.
I'm sure this shape has to do with avoiding tail strikes. But is seems to me like it also incurs negative lift. Does the tail draw air upwards, creating a reaction force in the downwards direction and thus negative lift?

Doesn't "jumbo jet" refer specifically to the 747? That picture is not a 747.

Yep. This is all, but not a "jumbo jet".

@HenningMakholm Usually so, but it has occasionally also been used to refer to wide-body jets in general (and the 777 certainly qualifies as that.)

Hmm i thought jumbo could refer to any wide body passenger plane. Guess not. Interestingly I almost picked the 747 for the pic, but decided on the 777 at the last minute just to be different. Good thing or else I wouldn't have learned this.

Indeed, according to wikipedia a “Jumbo Jet” is a synonym for any wide-body aircraft. That was new to me either and doesn't coincide with my experience. But they also say the B747 is the Jumbo Jet whereas the others have prefixes (like super- and mini-). Btw: Joe Sutter - the 747's father - died only 6 months ago (Aug 2016) at the age of 95. I've read he didn't like the name "Jumbo" for "his" plane, but I cannot find any evidence right now.

And Boeing did advertise the B747SP as a Junior Jumbo.

You are right, the upsweep at the tailcone allows the pilot to rotate the aircraft during take-off and landing without touching the ground with the rear fuselage. When such a tail strike  happens, the aircraft needs to be inspected and repaired, and incorrect repairs after a tail strike have already caused loss of life.
While most Boeing fuselages show some downslope of the upper tailcone contour, this effect is even more pronounced with all Airbus aircraft except the A380. There the upper contour of the tailcone is straight. Military transports with a rear ramp show even more upsweep to keep the heavy ramp short, and most need additional strakes to limit the area of separated flow there at low speed.
This upsweep adds a small downforce and, since it happens away from the c.g., a pitch-up moment. First, at the transition from the cylindrical section to the tailcone you find a strong suction peak at the high curvature region on the lower fuselage. Also, the lower side of the tailcone has a lower pressure than the upper side. Both create the downforce and the pitch-up moment. However, a three-dimensional body of a very low aspect ratio like the fuselage has a very low lift curve slope, so even the strong upsweep creates a small moment when compared to the contribution of the horizontal tail surface.
The local flow at the tail is dominated by the wing wake. To create lift, the wing has to deflect the flow downwards, and this produces a local flow direction at the tailcone which aggravates the situation created by the upsweep. The best indication for the local direction of flow is the rain diverter above the rear fuselage door. See below the rear door of the A320: To create the lowest possible drag, the rain strip is aligned with the local direction of flow during cruise. When flying at lower speed, the downwash is even stronger.

A320 rear fuselage (own work, based on this source)

The term 'jumbo jet' refers specifically to the Boeing 747 (family). A380 is sometimes called superjumbo; the image shows a Boeing 777, which is not a jumbo.
As far as the flow over the fuselage is concerned, the flow does accelerate over the bottom rear fuselage as a result of the shaping; however, the effects of the horizontal stabilizer is predominant in this region and the effect of the fuselage in the net force produced is negligible.
As can be seen from the figure, the fuselage narrows not only from bottom up (to prevent tail strike), but also on the sides (as seen in the top view) to provide a steamlined body. The net result is that the flow is three dimensional- up and towards the centre of symmetry. In some aircraft (usually cargo ones), where the fuselage upsweep is pretty steep for loading and rotation purposes, the resulting crossflow and boundary layer growth can sometimes lead to flow seperation
In case of commercial airliners, the horizontal stabilizer acts as an inverted wing- the result being accelerated flow over the bottom side of the fusealge in the region. This is the most significant reason for the flow in the rear end of the fuselage, resulting in a 'negative' lift over the tail-plane region. However, if the whole fuselage is considered, it provides some positive lift.

The entire tail (including the horizontal stabilizer) designed to have negative lift. So the negative lift on from the tail cone is not a big deal.
This is to create a pitch-up moment to pull the nose up which increases overall lift.

I don't the OP is asking about the horizontal stabilizer but rather effect of the fuselage shape on lift.

@habu This answer isn't talking about the horizontal stabilizers, either, but rather the entire tail section of the aircraft (including the horizontal stabs and the aft portion of the fuselage.)

The negative lift is only for stability. It decreases overall lift. Yes, it pitches up the nose, but only to counteract the pitch-down moment resulting from the CG location.

In general a simple tapered body at an angle of attack will net zero lift, with the front pulling up and the back pulling down, resulting in a nose up torque.

When a body generates aerodynamic force, most of that force will be generated very close to the leading edge, as that is where the center of pressure is located. Relatively little is happening at the trailing edge, with respect to the generation of pressure differentials - you do still need to pay attention to the trailing edge in order to ensure that airflow is smooth and doesn't 'separate', but it's not the first place you should be looking to determine if the body, as a whole, will generate lift.
FWIW, a lot of modern aircraft fuselages are designed as lifting bodies, in order to help improve efficiency and performance, so, on the whole, they will be generating some amount of lift throughout most, if not all stages of flight.


text:
What is the difference between a monocoque and semi-monocoque fuselage type?
What are the main differences between these two types of fuselages?

A monocoque fuselage has its skin holding the skeleton structure together while the semi-monocoque has both the skin and the skeleton holding together. Semi-monocoque also has "stringers" running horizontally down the plane to help hold the frame together. The monocoque fuselage also cannot be used for airframes after a certain size (small aircraft with single engine), but the semi-monocoque has been used from single piston engines to commercial airliners.
A monocoque design would also have a safety risk involved if the skin was damaged because it is the load-bearing structure.

Image and some text source

A semi-monocoque design also has a safety risk involved if the skin is damaged, because it is still a load-bearing structure.

The main difference between the two is the way the loads are carried by the aircraft structure.
The earliest aircraft had an underlying truss structure that carried the load, with fabric covering this load bearing skeleton. The outer shell carried no loads and from the structural viewpoint, was basically dead weight. The image below shows the underlying structure of the Blériot XI

By J.Klank - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=7219409
Later, the aircraft structure was designed so that the the skin itself was a mainload carrying member. This type of construction was called the monocoque, which is a French term for single shell (or hull). A good example is the fuselage of the De Haviland Mosquito (which is all the more impressive as it was made of plywood). The fuselage was made in two monocoque halves, which were joined together, which can be seen in the following figure.

De Haviland Mosquito monocoque structure- image from pistonwings.tumblr.com
As the skin carries the entire load, the strength requirements mean that this technique cannot be used for aircraft beyond a certain level. For thin skinned structures, buckling is critical issue, which affects the load carrying capcity. Large structures can be made that can carry load only via the skin, but support is still required. For example, the fuel tanks of Altas ICBMs carried the entire load on the skin, but required internal pressure to maintain the shape, without which they collapsed.
The semi-monocoque is in between the above two- here, a stressed skin is used that takes some of the load, but is reinforced by the underlying structure, which also takes load. Basically, both the skin and the underlying structure share the load. Most of the aircraft today use this type of construction, from small GA aircraft to the large commercial airliners. For example, the image below shoes a fuselage section of Airbus A350XWB, which features this type of construction.

Image from a350xwb.com

As the skin carries the load, the strength requirements mean that this technique cannot be used for aircraft beyond a certain level. Most of the aircraft today use this type of construction. Something's missing there - which is this type of construction that most aircraft use today? Also, can you expand on the certain level that, once exceeded, prevents the use of monocoque construction?

@FreeMan You're correct. Quite a large chunk is missing. I've edited it. Thanks for catching.

Makes much more sense now!  :)


text:
How do the oxygen masks deploy after a cabin decompression?
Is there any sensor incorporated on the Passenger Service Unit that tells the masks to deploy when a cabin decompression occurs?

According to this Airliners.net forum post,

The masks are deployed automatically (typically when cabin altitude exceeds 14,000 feet), or can be deployed manually from the flight deck. In addition, if a passenger service unit oxygen door should fail to open, cabin crew can open the PSU door (either inserting a flat object or a special tool depending on the aircraft type) manually.

So basically, the masks are deployed automatically based on sensors, with manual deployment as a primary failsafe and physical access as a secondary failsafe.

For completeness, many types have a manual override in the cockpit should the automatic deployment fail for whatever reason.  Examples can be seen in the answers to this question.


text:
Why does one of the Boeing 777's spoilers deploy differently from the rest?
There is one spoiler that isn't totally deployed. Look:

Source: Airliners.net
And also on this other picture:

Source: Airliners.net
Why aren't they deployed at the same angle?

Roll control is provided by 2 flaperons, 2 ailerons, and 14 spoilers.
Spoiler panels 4 and 11 are controlled mechanically rather than electrically. They are driven directly from control wheel deflections via a control cable. In case of compete electrical loss, limited roll control is available until the electrical system is restored.  This probably explains the difference in rigging.
Spoiler panels 4 and 11 are also used as speedbrakes, both in the air and on the ground. The speedbrake function for this spoiler pair only has two positions: stowed and fully extended. The speedbrake commands for spoilers 4 and 11 are electrical in nature, with an ACE (actuator control electronics) giving an extend or retract command to a solenoid operated valve in each of the actuators.
Once that spoiler pair has been deployed by a speedbrake command, there is no control wheel speedbrake command mixing, as there is on all the other fly-by-wire spoiler surfaces.
Boeing B-777: Fly-ByWire
Flight Controls

Follow-up question: Why are spoilers, rather than ailerons, used as the mechanical backup controls?

@tas That is an interesting question. I recommend asking it. :) You can link back to this question for context, if you want.

In roll control, all spoilers except for 4 and 11, are fly-by-wire. Spoilers 4 and 11 receive mechanical signals for roll control. For spoilers 4 and 11, a cable system connects the control wheels to the spoiler PCUs. Cable movement supplies a mechanical input to the PCUs which move the spoilers. The movement of the PCU housing supplies mechanical position feedback.
In speedbrake control, all spoilers are fly-by-wire, including spoilers 4 and 11. For spoilers 4 and 11, speedbrake control is only available in normal mode. When the pilot moves the speedbrake lever more than 54 degrees, the PFC commands the ACE to send an ON/ OFF electrical signal to the two spoiler PCUs.

Am I missing something that differentiates this answer from the previously accepted answer? It seems very similar, and the post would probably be better served by editing the accepted answer to provide additional context.


text:
Why is the bypass ratio of a turboprop higher than turbofan?
Whenever, I come across turboprop, the author always mentions that they have higher bypass ratio than turbofan but no one explains the reason for this.
So, is the bypass ratio higher due to higher disc radius of turboprop or is it due to less air flow through the core or the combination of both?
If it is only due to less air flow inside the core, then they can still have a higher bypass ratio in turbofan right? (Since advanced turbofan produce less noise due to the nacelle)

When you say "propellor" do you mean a piston engine, or a turboprop or both?

I've never heard anyone refer to a bypass ratio in reference to a prop. The ratio is the amount of intake air that does not enter the core vs the air that does. Without a ducted system I don't know if you can really come up with an amount of air though the prop

Related: The fan/propeller speed aspect is developed in the answer of Is it possible to drive a turboprop directly from a jet engine without a gearbox?

I seem to recall the big difference between the two is that the prop is generally bigger than the fan, but that the prop also has an effect where it's not just the air going through the prop that adds to the thrust, but the air immediately surrounding the prop too. I believe this additional air is included in the BPR calculation but I can't remember the name of the effect.

Bypass ratio is the ratio of the overall flow  to the core flow (which goes eventually through the combustion chamber). Overall flow is either the flow captured by the intake or going through the propeller disc. Even for piston aircraft it is possible to define a bypass ratio if you interpret the air which flows through the cylinders as the core flow.
A turbofan essentially uses a shrouded propeller of high solidity (or activity ratio) which helps to accelerate the flow through it as much as possible. It needs to produce the most thrust from the limited air volume captured by the shroud's intake. The limitation is needed to limit the tip speed of the fan and the overall size and drag of the shroud.
Propellers, on the other hand, accelerate a bigger flow by less and need to cover less of the propeller disc for doing this. To keep thrust constant, a bigger mass flow needs to be involved into the acceleration.

Plot of the thrust specific fuel consumption in lb of fuel per lb of thrust per hour of different engines over the logarithm of their bypass ratio (picture source).
A comparison is only sensible if we look at the same core component: If a turbofan and a turboprop share the same high pressure components. One example would be the Rolls-Royce/Allison 2100 and the Rolls-Royce/Allison 3007. Wikipedia gives the mass flow of the 3007 as 109 - 127 kg/s but gives no information for the 2100. Using the maximum flight speed of the Alenia C-27J of 167 m/s and its propeller diameter of 4.15 m, we can find a lower bound for the mass flow through one of its propellers if we make the heroic assumption that the maximum speed is reached in 25000 ft (7620 m) where air density is 0.55 kg/m³.
Mass flow through the propeller of one 2100 is at least 1242.4 kg/s or about ten times of what it is for the 3007. The mass flow though the core is the same because both engines share the same hot section. The static thrust of the 2100 is higher than that of the 3007 but drops more quickly with speed, so at high speed the 3007 produces more thrust.

I have a doubt. If mass flow through turbofan is limited due to shroud and this is the reason for lower bypass ratio (than propeller), why don't we remove this conventional shroud and fit a shroud which only starts from the fan disc (more like a ducted fan but the duct extending till the rear nozzle)?

@Selva: No, the shroud helps to make the flow uniform. Without it the fan could not be optimised to the extent possible, and thrust per frontal area would need to be lower. The part ahead of the fan face is the most important. Maybe this answer helps. Or this answer.

Thx for the reply and I apologise for asking too many questions. Wikipedia says RR2100 has 28.7in diameter and RR3007 as 38.5in. So, clearly 2100 has lower diameter (right?). Then, What is the reason for higher mass flow in 2100 (is it due to solidity?). Moreover, after reading your other answers I have a new doubt. Why fan in turbofan has more thrust than prop? Isn't it should be other way around? Because the turbofan also generates thrust from jet.

@Selva: The 5:1 bypass ratio of the 3007 requires a fan, while the 2100 has an added compressor stage in its place which is only sized for the core flow. The fan is like the propeller, but then the 2100 would have 4.15 m diameter. Thrust varies with speed, and more so for a propeller than a jet. If you look at static thrust (at zero speed), the 2100 has more. When I say in the other answer that the fan has more thrust than a prop, I mean this per area.

Oh. Got it now. Again, thanks a lot for your reply :)

There is a limitation when designing a fan, the speed at the tip to not reach sonic conditions. Essentially, that means that is basically rotational speed times diameter of the blade. So... at same conditions the factor of rotational speed and diameter of the blade will be a design condition.
That is coming up with 2 different design solutions:

We design a fan that we connect directly the fan to the turbine. So higher rotational speed of the fan but smaller balde diameter.
We install a reduction gear, so we reduce the rotational speed of the fan and we can increase the diameter.

It is a simplification, but essentially the first is call turbofan and the second turboprop.
By design, the turboprop will have higher diameter and so higher bypass ratio but will carry a heavy reduction gear. So... we have a tradeof.
That is why some low subsonic airplanes prefer turboprop in comparison to turbojet.

Fan tips quite regularly go supersonic


text:
How large and heavy is the B737's built-in stair?
Some version of B737 have built in stair, which allows passengers boarding and exit without jet bridge or stair car.
How much do the stair systems weigh? And how much volume do they occupy?

A number of 737s are fitted with forward airstairs (and aft ones too). The Boeing Airplane Planning Document gives the airstairs opening as 0.41 X 1.12m, while the airstairs can be folded to less than 2.5m length. This should give the volume occupied by the airstairs.

Image from Boeing 737 Airplane Characteristics for Airport Planning document.
According to an article in aviationpros, the total system weighs in around 200 lbs:

Aircraft such as the DC9, MD80, MD90, and 737 aircraft have had a long enough history that many of them were built with the forward passenger air stair assembly. Many aircraft were also converted to non-airstair versions Ñ a 200+ lb. weight savings for the operator.


text:
Was this flight a fuel emergency?
Yesterday I flew from San Diego to Boston in a commercial 737 operated by Alaska Airlines. Before landing we spent almost an hour circling. When we finally landed, many passengers were surprised to learn that we were not in Boston; we were still 90 miles / 150 km away.
The flight attendants told us the pilots had been too busy to announce the diversion. When the captain finally made an announcement on the ground, he said we had been redirected because the wait for Boston was 60 minutes and "we only had about 10 minutes of fuel left."
The cause was snow in Boston. Many flights were cancelled. However, visibility was excellent where we were and the flight was smooth. So I was surprised that we were diverted.
According to flightaware, we started circling at approximately 4pm; we were diverted at 4:48pm and landed at BDL at 5:03pm. Our scheduled arrival time was 5:06pm. (We departed on time.)
Below is the flight path (source).
I was hoping that some people more knowledgeable than myself could help me better understand what was going on.

Does "10 minutes of fuel left" mean 10 minutes until empty or 10 minutes until it becomes urgent? I find it hard to believe that there was so little reserve fuel, especially given that we were in the air for the scheduled amount of time.
Would this situation count as a fuel emergency? Was it comparable to this incident?
How low do commercial jets normally go fuel wise? In particular, how common is it to have 10 minutes of fuel left when landing?
Can I find out more information about my flight online? I only know of flightaware. Is it possible to find ATC radio recordings?

Had I been the captain making that announcement, what I would have been saying was that at the point I diverted, we had 10 minutes of the fuel left that had been loaded for purposes of getting to Boston and doing any necessary holding. So at that point in the tanks there was 10 minutes of flying time fuel plus the fuel required to get to the filed alternate, plus the required reserve after that. What I would have been doing was diverting to the alternate 10 minutes before I was required to so for the simple reason that I was going to have to wait for 50 minutes beyond that time. No emergency.

@Terry Thanks. So you are saying the pilot meant "we had about 10 minutes of holding time left." That sounds reasonable to me.

You can normally find ATC recordings at liveatc.net. Funnily enough, their KBOS feeds are down right now because a cable got cut due to the snowfall (I guess from a plow or ice accretion on aerial lines/tree branches.) If you post a separate question regarding finding the ATC recordings, you can probably get better help finding the right feed(s) than leaving it combined with all of these other questions. By the way, welcome to Aviation.SE!

To summarize: When starting the hold, the captain was at about equal time from KBOS and KBDL (10 mn). He holded for a certain amount of time. When he had 80 mn of fuel in tanks, he was informed that he would have to wait 60 mn more. He calculated he would land with fuel in tanks for 10 mn (which would be used to taxi). He decided to fly to KBDL alternate, where he likely landed with 70 mn fuel left. Without holding time for KBOS he would have had the same quantity when landing at KBOS. Nothing seems wrong or related to an emergency here.

Thanks for the great answers. It sounds like the captain just chose his words poorly.

You can go onto flightradar24.com to find flight history as well, but no ATC recordings.

10 minutes before  'minimum' fuel estimate for landing, including contingency, not 10 minutes before they run out of fuel! If it ever got to '10 minutes left', then yes that constitutes an emergency. This is an extremely rare, and very reportable situation that would be gone over with a fine-tooth comb afterwards. In Australia (at least) the regulator would be notified and would raise a case investigation over it. MH got into trouble at LHR years ago for cutting fuel load to minimums, then 'requiring' a landing slot/runway from controllers due to low fuel. They got into big trouble!

There appears to be no emergency. The flight was diverted at 16:58 EST and landed at Bradley International Airport at 17:03 EST. The same flight on 6th Feb landed at Boston at 16:46 EST. So basically, the flight was in the air only for an extra 15 minutes, compared to the scheduled time.
According to § 121.639 Fuel supply: All domestic operations.:

No person may dispatch or take off an airplane unless it has enough fuel—
(a) To fly to the airport to which it is dispatched;
(b) Thereafter, to fly to and land at the most distant alternate airport (where required) for the airport to which dispatched; and
(c) Thereafter, to fly for 45 minutes at normal cruising fuel consumption

So basically, the pilot diverted because the holding time was another 60 minutes and that would've eaten into fuel reserves.

I think the captain meant that the aircraft had only 10 minutes of fuel till he had to dip into reserves (or fly the alternate- it depends) and diverted because of the 60 minute waiting time. He could've been more clear though.

The pilot would've declared a fuel emergency if there was one. So, I think there was none.

Its quite uncommon for aircraft to land on 10 minutes of reserve fuel, though it has happened. In fact, some aircraft have run out of fuel.

You can find details about the ATC in liveatc's audio archives.

What is the "where required" qualifier in the 121.639 section for? Are there situations where filing an alternate is NOT required?

@curious_cat Yes. There are situations where filing an alternate is not required. See this questio and this aopa document

I feel like this was just a poor choice of wording by the captain.
It is extremely rare for an aircraft to land with just 10 minutes of fuel remaining, though it has happened before. In most cases, a jet needs to land with at least 30 minutes of fuel in the tanks, plus a variable percentage on top depending on the trip length - plus the airline-specific Ops Specs may require even more, and sometimes a specific airport warrants extra fuel for holding purposes. If the weather doesn't look too good, the plane needs to carry even more fuel to reach another airport, without using these minimums.
So I suspect the pilot meant he had 10 minutes of holding time, before he would have dipped into these minimums. Doing so is a big no-no and the authorities will need to be notified, hence the diversion before that happened. If my suspicion is correct, this did not count as an emergency.
As for your last question, liveatc.net is where you can find most ATC recordings. And if I am wrong and the pilot meant there was 10 minutes of fuel in the tanks, you should see the details on avherald.com soon!


text:
What names are used for certified "mechanics"?
While watching a documentary on the the UK Red Arrow aerobatic team, mechanics were sometimes called "tradesmen", "technician", or "engineer".
In the US they are commonly called "aircraft mechanics" or an "A&P".
What other designations are used for certified aircraft "mechanics"?

image source

Not sure if you realize or not, but you don't have to be certified to work on an aircraft, so "technician" could be relatively accurate, as well as "tradesmen". I'm not sure "engineer" would be accurate though. The requirement (at least in the US) is that anybody can work on an aircraft but it must be done under the supervision of a certified A&P for the work performed, and the A&P is the only one who can sign off. Rules are a little different for home built aircraft though.

I am a Pilot & A&P :)

The British seem to use the word "engineer" in many places that we Americans would use the word "mechanic". Not wrong by any means, just different ("lift" == "elevator", "lorry" == "truck", etc)

What names?  I've worked with Robert, Amanda, Matt, Michelle, Felipe, Leon....  The names are very multi-cultural and varied!  All joking aside, good question.  :)

Generally in the British Commonwealth it's Aircraft Maintenance Engineer.  In Canada an AME can do maintenance up to and including an annual condition inspection or other major inspections, but has to be specifically endorsed on more complex aircraft to sign off any kind of work.
In the US the main classification is Airframe and Power Plant Mechanic (A&P), who can do and sign maintenance releases on any aircraft without an endorsement.  However to sign off an annual condition inspection or other major inspections, the mech needs an IA, or Inspection Authorization.

to make matters more confusing, AME can also mean Aero Medical Examiner, used by EASA and FAA both.

14 CFR Part 65 Subpart D refers to it as a mechanic certificate.  Airframe and Powerplant are two separate ratings applicable to the mechanic certificate.  There are also Repairman certificates under Subpart E which are for workers at manufacturers and repair stations.

The Repairman cert is also for unlicensed people to work on homebuilts if I recall.  Used to be only the original builder got one but now any owner can get one if they take a course.  The rules in Canada for maintaining homebuilts are actually a bit more liberal; whoever's name is on the C of R can sign any maintenance release on a homebuilt, including annuals.

In the US, an A&P can sign off on a condition inspection (experimental and Light Sport) as well as 100 hour inspections. An IA (A&P with Inspection Authorization) is required to sign off on annual inspections on certificated aircraft.

From Wikipedia:

An Aircraft Maintenance Engineer (AME), also Licensed Aircraft Maintenance Engineer (LAME or L-AME), is a licensed person who carries out and certifies aircraft maintenance. The license is widespread internationally and is recognised by the International Civil Aviation Organization (ICAO).

Which LAME pissed of the guy making those titles?

Make sure you hire the right type of AME. You can't have the same AME issue your medical and do your annual inspection.


text:
Is it harmful to operate an engine "over square"?

Never Fly Your Engine "Oversquare!" is an old recommendation. This wisdom cautions pilots that selecting a power setting with a manifold pressure in inches higher than the RPM in hundreds is damaging to the engine -- e.g., 2300 RPM dictates using no more than 23 inches manifold pressure.
Pilots are instructed by flight instructors to always reduce the manifold pressure before the RPM on power reductions, and increase the RPM before the manifold pressure on power increases. From this, it seems even short periods of "oversquare" is harmful during takeoff and landing. What about cruise?
Is it harmful to operate an engine for long periods "over square"?

This question is not about a rule of thumb or generalized operation of an engine. It is about a specific setting of the engine controls.

It says in the accepted answer "It actually may be beneficial to run an engine "oversquare" in some cases!" and goes on to further explain.

No it's an old pilots' spouse's tale.  Those are just two numbers.  Having said that, Brake Mean Effective Pressure in the cylinder is higher when manifold pressure is high and rpm is low, for a given horsepower output, than the opposite way around, so there is a bit more stress on the cylinder head and piston.  And you do want to avoid that condition at the extremes to avoid really excessive BMEP, which could result in detonation.
The key word is "extremes".  With wide open throttle with the propeller at min RPM, it could be damaging, so it is normal practice to always lead with rpm on the way up and throttle on the way down.
But in the normal operating range it's not a big deal.  Look at a supercharged engine like a R985.  Redline is 36" of manifold pressure at 2200 or 2300 rpm.  It's jugs should be blowing off left and right.  And you cruise it at maybe 28" and 1600.  Oversquare enough?
So on the one hand you do have lower BMEP running higher rpm/lower MP, so somewhat lower stress on the cylinder.  On the other hand, heat and wear from friction is higher because of the higher rpm itself (and very importantly, the higher piston speed), so that tends to favour higher MP/lower rpm, for the same horsepower output.  My own preference in a normally aspirated engine is to cruise at say 2000 rpm and 22" instead of the other way around, because there is more benefit from the lower piston speed (piston rings wear out after traveling a specific distance, so the lower the piston speed the better, within reason) than from marginally lower internal cylinder pressures.

It’s an old wives tale about reciprocating engines, similar to shock cooling and a 1001 other ignorant myths perpetuated by misinformed pilots.  I’ve also heard this as ‘prop on top’ as well.  The idea was to prevent overstressing the engine at high power settings with a high load applied, but it does not necessarily mean one can not operate an engine that way.  Consult the power charts published in your airplane’s POH or engine manual for the correct range of power settings.
When reducing power, the generally recommended procedure is to reduce MAP to a cruise power setting, then adjust the propeller speed, then make a final adjustment to the MAP to compensate for changes in power output due to the increased workload.  The process is reversed when increasing power.

I strongly disagree with the shock cooling part.  That does cause damage.  Lycoming has a maximum cool down rate (if I recall it's about 3 degC/sec).  It's all from the cylinder head casting shrinking faster than the valve seats which creates massive hoop stress in the casting around the seats and generally will cause cracks between the exhaust valve and spark plug hole.  Glider tugs experience shock cooling more than any other airplane because of the full power climb then sudden descent on every flight.  Glider clubs all use power reduction procedures now to mitigate it.

On the other hand, you can't "shock heat" a cylinder, because the differential expansion is the other way around and can't cause a crack.  So it's no problem adding large amounts of power, if the engine can handle it without stumbling.

I have never once in my life witnessed a shock cooled engine on an aircraft.  And this comes from experience dealing with twins like Dutchesses and Seminoles which have engines routinely shut down during flight for training purposes.  We don’t see a change in TBOs for each engine.  I suppose if you ran an aircraft engine on a load cell for 45 mins to heat soak it, then quickly dunked the crankcase into a vat of ice water, there’s a chance of shock cooling, but during normal operations, the answer is no.

Training airplanes don't come close to the duty cycle that glider tugs do. A glider club I was in was plagued with cracked cylinders and did a series of instrumented tests and found that WOT to idle exceeded Lycoming's 50F/min cooling rate.  After a power step down procedure was adopted, the problems went away.  I'll admit it's not common on normally operated aircraft, but don't say it can't happen or that it's not hard on a cylinder to cool it suddenly.  The stresses I talked about are there; they're not imaginary.  https://www.lycoming.com/content/how-avoid-sudden-cooling-your-engine.

The problem is that cracked cylinder heads are more like kelt caused by high CHTs than shock cooling of an engine.  And this would simply indicate an engine which has been extensively operated at high power settings at low airspeeds for prolonged periods, decreasing the engine life and resulting in these maladies.  Again, if shock cooling were a root cause here I would expect to see a lot more damage to engines in light twins regularly used for engine out and restart procedures as that is literally the worst case scenario for a shock cooled engine.  Is it shock cooling? Maybe, but I doubt it.